#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <ctype.h>
using namespace std;

const int basesize = 1024;
const int argvnum = 64;
const int envnum = 64;
// 全局的命令⾏参数表 
char *gargv[argvnum];
int gargc = 0;
// 全局的变量 
int lastcode = 0;
// 我的系统的环境变量 
char *genv[envnum];
// 全局的当前shell⼯作路径  
char pwd[basesize];
char pwdenv[basesize];

// 全局变量与重定向有关 
#define NoneRedir 0
#define InputRedir 1
#define OutputRedir 2
#define AppRedir 3
int redir = NoneRedir;
char *filename = nullptr;
//去除空格
#define TrimSpace(pos) do{\
	while(isspace(*pos)){\
		pos++;\
	}\
}while(0)

string GetUserName()
{
	string name = getenv("USER");
	return name.empty() ? "None" : name;
}
string GetHostName()
{
	string hostname = getenv("HOSTNAME");
	return hostname.empty() ? "None" : hostname;
}
string GetPwd()
{
	if(nullptr == getcwd(pwd, sizeof(pwd))) 
		return "None";
	snprintf(pwdenv, sizeof(pwdenv),"PWD=%s", pwd);
	putenv(pwdenv); 
	return pwd;
}
string LastDir()
{
	string curr = GetPwd();
	if(curr == "/" || curr == "None") 
		return curr;
	size_t pos = curr.rfind("/");
	if(pos == std::string::npos) 
		return curr;
	return curr.substr(pos+1);
}
string MakeCommandLine()
{
	char command_line[basesize];
	snprintf(command_line, basesize, "[%s@%s %s]# ",\
	GetUserName().c_str(), GetHostName().c_str(), LastDir().c_str());
	return command_line;
}
void PrintCommandLine() // 1. 命令⾏提⽰符 
{
	printf("%s", MakeCommandLine().c_str());
	fflush(stdout);
}
bool GetCommandLine(char command_buffer[], int size) // 2. 获取⽤⼾命令 
{
	char *result = fgets(command_buffer, size, stdin);
	if(!result)
		return false;
	command_buffer[strlen(command_buffer)-1] = 0;
	if(strlen(command_buffer) == 0) 
		return false;
	return true;
}
void ResetCommandline()
{
	memset(gargv, 0, sizeof(gargv));
	gargc = 0;
	// 重定向 
	redir = NoneRedir;
	filename = nullptr;
}
void ParseRedir(char command_buffer[], int len)
{
	int end = len - 1;
	while(end >= 0)
	{
		if(command_buffer[end] == '<')
		{
			redir = InputRedir;
			command_buffer[end] = 0;
			filename = &command_buffer[end] + 1;
			TrimSpace(filename);
			break;
		}
		else if(command_buffer[end] == '>')
		{
			if(command_buffer[end-1] == '>')
			{
				redir = AppRedir;
				command_buffer[end] = 0;
				command_buffer[end-1] = 0;
				filename = &command_buffer[end]+1;
				TrimSpace(filename);
				break;
			}
			else
			{
				redir = OutputRedir;
				command_buffer[end] = 0;
				filename = &command_buffer[end]+1;
				TrimSpace(filename);
				break;
			}
		}
		else
		{
			end--;
		}
	}
}
void ParseCommand(char command_buffer[])
{
	const char *sep = " ";
	gargv[gargc++] = strtok(command_buffer, sep);
	// =是刻意写的 
	while((bool)(gargv[gargc++] = strtok(nullptr, sep)));
	gargc--;
}
void ParseCommandLine(char command_buffer[], int len) // 3. 分析命令 
{
	ResetCommandline();
	ParseRedir(command_buffer, len);
	ParseCommand(command_buffer); 
}
void DoRedir()
{
	// 1. 重定向应该让⼦进程⾃⼰做！ 
	// 2. 程序替换会不会影响重定向?不会 
	// 0. 先判断 && 重定向 
	if(redir == InputRedir)
	{
		if(filename)
		{
			int fd = open(filename, O_RDONLY);
			if(fd < 0)
			{
			   exit(2);
			}
			dup2(fd, 0);
		}
		else
		{
			exit(1);
		}
	}
	else if(redir == OutputRedir)
	{
		if(filename)
		{
			int fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0666);
			if(fd < 0)
			{
				exit(4);
			}
				dup2(fd, 1);
			}
		else
		{
			exit(3);
		}
	}
	else if(redir == AppRedir)
	{
		if(filename)
		{
			int fd = open(filename, O_CREAT | O_WRONLY | O_APPEND, 0666);
			if(fd < 0)
			{
				exit(6);
			}
			dup2(fd, 1);
		}
		else
		{
			exit(5);
		}
	}
	else
	{
	// 没有重定向,Do Nothong! 
	}
}
// 在shell中 
// 有些命令，必须由⼦进程来执⾏ 
// 有些命令，不能由⼦进程执⾏，要由shell⾃⼰执⾏ --- 内建命令 built command 
bool ExecuteCommand() // 4. 执⾏命令 
{
	 // 让⼦进程进⾏执⾏ 
	 pid_t id = fork();
	 if(id < 0) return false;
	 if(id == 0)
	 {
		 //⼦进程 
		 DoRedir();
		 // 1. 执⾏命令 
		 execvpe(gargv[0], gargv, genv);
		 // 2. 退出 
		 exit(7);
	 }
	 int status = 0;
	 pid_t rid = waitpid(id, &status, 0);
	 if(rid > 0)
	 {
	 	 if(WIFEXITED(status))
		 {
		 	lastcode = WEXITSTATUS(status);
		 }
		 else
		 {
		 	lastcode = 100;
		 }
	 	return true;
	 }
	 return false;
}
void AddEnv(const char *item)
{
	int index = 0;
	while(genv[index])
	{
		index++;
	}
	genv[index] = (char*)malloc(strlen(item)+1);
	strncpy(genv[index], item, strlen(item)+1);
	genv[++index] = nullptr;
}
// shell⾃⼰执⾏命令，本质是shell调⽤⾃⼰的函数 
bool CheckAndExecBuiltCommand()
{
	if(strcmp(gargv[0], "cd") == 0)
	{
		// 内建命令 
		if(gargc == 2)
		{
			chdir(gargv[1]);
			lastcode = 0;
		}
		else
		{
			lastcode = 1;
		}
		return true;
	}
	else if(strcmp(gargv[0], "export") == 0)
	{
		// export也是内建命令 
		if(gargc == 2)
		{
			AddEnv(gargv[1]);
			lastcode = 0;
		}
		else
		{
			lastcode = 2;
		}
		return true;
	}
	else if(strcmp(gargv[0], "env") == 0)
	{
		for(int i = 0; genv[i]; i++)
			printf("%s\n", genv[i]);
		lastcode = 0;
		return true;
	}
	else if(strcmp(gargv[0], "echo") == 0)
	{
		if(gargc == 2)
		{
			// echo $?
			// echo $PATH
			// echo hello
			if(gargv[1][0] == '$')
			{
				if(gargv[1][1] == '?')
				{
					printf("%d\n", lastcode);
					lastcode = 0;
				}
			}
				else
				{
					printf("%s\n", gargv[1]);
					lastcode = 0;
				}
			}
			else
			{
				lastcode = 3;
			}
		return true;
	}
	return false;
}
// 作为⼀个shell，获取环境变量应该从系统的配置来 
// 我们今天就直接从⽗shell中获取环境变量 
void InitEnv()
{
	extern char **environ;
	int index = 0;
	while(environ[index])
	{
		genv[index] = (char*)malloc(strlen(environ[index])+1);
		strncpy(genv[index], environ[index], strlen(environ[index])+1);
		index++;
	}
	genv[index] = nullptr;
}
int main()
{
	InitEnv();
	char command_buffer[basesize];
	while(true)
	{
		PrintCommandLine(); // 1. 命令⾏提⽰符 
		// command_buffer -> output
		if( !GetCommandLine(command_buffer, basesize) ) // 2. 获取⽤⼾命令 
			continue;
		ParseCommandLine(command_buffer, strlen(command_buffer)); // 3. 分析命令 
		if ( CheckAndExecBuiltCommand() )
			continue;
		ExecuteCommand(); // 4. 执⾏命令 
	}
	return 0;
}
